water coming out from the reservoir tank

Good morning, thanks for being there always. I have a 2003 lexus ES300 I notice working comes out from the reservoir breathing cap hose when d car is hot. There is no sign of leakage when the car is parked on ground. But it spills water when it hot from the reservoir cap cover, it comes like a Lil drop from it. The car doesn't over. I also notice the hose inside the reservoir thanks becoming whitish when this happen. But immediately the engine cools off. It stops dropping.. what's d cause pls